WO1987007092A1 - Reflecteur strie et procede pour laser a electrons libres - Google Patents

Reflecteur strie et procede pour laser a electrons libres Download PDF

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Publication number
WO1987007092A1
WO1987007092A1 PCT/US1987/000671 US8700671W WO8707092A1 WO 1987007092 A1 WO1987007092 A1 WO 1987007092A1 US 8700671 W US8700671 W US 8700671W WO 8707092 A1 WO8707092 A1 WO 8707092A1
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WO
WIPO (PCT)
Prior art keywords
wave
corrugations
waveguide
blazed
wavelength
Prior art date
Application number
PCT/US1987/000671
Other languages
English (en)
Inventor
Robin J. Harvey
Original Assignee
Hughes Aircraft Company
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Hughes Aircraft Company filed Critical Hughes Aircraft Company
Priority to DE8787902965T priority Critical patent/DE3781089T2/de
Publication of WO1987007092A1 publication Critical patent/WO1987007092A1/fr

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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/09—Processes or apparatus for excitation, e.g. pumping
    • H01S3/0903—Free-electron laser
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
    • H01S3/06—Construction or shape of active medium
    • H01S3/063—Waveguide lasers, i.e. whereby the dimensions of the waveguide are of the order of the light wavelength
    • H01S3/0632—Thin film lasers in which light propagates in the plane of the thin film
    • H01S3/0635—Thin film lasers in which light propagates in the plane of the thin film provided with a periodic structure, e.g. using distributed feed-back, grating couplers

Definitions

  • the present invention relates generally to waveguide reflectors and specifically to a reflector for use in the resonating cavity portion of a free electron laser (FEL).
  • FEL free electron laser
  • Two-stage free electron lasers typically utilize magnetic mirrors at the opposite ends of their resonating cavities to reflect the pump field along the optical axis of the cavity.
  • a typical example of a free electron laser (FEL) is illustrated in U.S. Patent No. 4,438,513 issued in the name of Luis Elias and assigned to the United States of America. 1
  • An FEL operated in the microwave to far-infrared bands requires a high-Q resonator through which an electron beam must be passed.
  • the resonators therein will have to be overmoded, i.e., use quasi-optical propagation with cross sections larger than a half wavelength to avoid thermal damage to the resonator structure.
  • the expanding Gaussian- mode patterns of a conventional confocal or a concentric 0 resonator do not easily fit within the bore of the wiggler- agnet array, especially at frequencies below 100 GHz.
  • the radiation fields of such conventional resonators must either be confined by some means along the 30-100 cm interaction length or 5 the resonator must be very large, on the order of 10 meters.
  • blaze- of-grating technique is an optics technique whereby ruled grooves of a diffraction grating are given a controlled shape such that they reflect as much as 80%
  • A. further object of the invention is to allow the generation of high power in an FEL.
  • the present invention in a broad aspect, is a corrugated reflector for coherent reflection of the power in a wave at a specified wavelength, having a hollow cylindrical member with a longitudinal axis, and
  • the blazed vane means are triangularly shaped corrugations configured so as
  • two such reflectors can be configured into a laser resonator by placing them at opposing ends of a matching waveguide.
  • the resulting reflector design is a much more compact and efficient apparatus than the conventional
  • the present -invention also encompasses ' a novel method for reflecting waves in a corrugated reflector such that the blazing condition is satisfied.
  • the present invention further encompasses a novel -* laser resonator cavity apparatus employing two of the blazed corrugated reflectors, as well as an FEL utiliz ⁇ ing such a cavity.
  • FIG. 1 shows a corrugated reflector according to 15 the present invention
  • FIG. 2 shows the retroreflective condition for operation of the reflector of FIG. 1;
  • FIG. 3 shows two of the reflectors of FIG. 1 configured as a resonator; 20 FIG. 4 shows the blaze condition for operation of the reflector of FIG. 1;
  • FIG. 5 shows the blaze condition for matching across the reflector of FIG. 1;
  • FIG. 6 shows an FEL incorporating reflectors 25 according to the present invention.
  • FIG. 1 a preferred embodiment of a blazed corrguated reflector 30 10 according to the present invention is shown in FIG. 1
  • the reflector comprises a hollow cylindrical member 12 utilizing internal corrugations or vanes 14 which are blazed to have specified design angles to coherently reflect power at specified wavelengths.
  • the corrugations are triangular and spaced apart in the transverse direction with intervening bases between them as shown in FIG. 5.
  • the reflector 10 must meet the following three conditions. First, there must be retroreflection for the Bragg condition for gratings. "Retroreflection” is, as known in the art, reflection wherein the reflected rays of radiation return along paths parallel to those of their corres- ponding incident rays.
  • Equation 3 Equation 3 combined with equation 1 gives:
  • Equation (2) indicates that, for the purpose of analysis of the reflector for FEL applications, the angles of the incident and reflected waves are presumed to be equal.
  • Equation (4) indicates that once any two of the quantities ⁇ , ⁇ , or d are known, the thrid parameter may be determined, arid therefore that the design may begin with any one of these three parameters .
  • k wave number of the travelling wave
  • 3 velocity of electrons ⁇ speed of light
  • k w wiggler wave number
  • v velocity of electrons
  • d distance between peaks of adjacent corrugations
  • ⁇ the angle between the direction of propagation of the wave and the waveguide wall.
  • the peaks of adjacent corrugations 14 are spaced at a distance d equal to the longitudinal half-wavelength of the mode to be reflected.
  • the waveguide mode is related to the inside radius of the waveguide 18, to which the reflector 10 is attached to form a resonator 16, as shown in FIG. 3.
  • the distance between the opposing bases 17 of the corrugated reflector as shown in FIG. 5 is selected to equal the waveguide diameter 2r, and are aligned as later discussed for ideal matching of the waveguide modes.
  • the blaze angle cond ition may be stated as :
  • k c is the cut-off wave number of the waveguide.
  • the propagation of the standing and travelling wave modes can be analyzed as the progagation of partial waves, each partial wave travelling through the waveguide in a particular direction
  • These partial waves arrive at a well-defined angle to the surface of the waveguide.
  • a partial wave reflects and forms a complement of itself travelling at the same angle, but away from the surface.
  • This well-defined angle is herein referred to as the angle of the partial wavefront.
  • FIG. 4 indicates how the blaze condition is met.
  • the corrugations 14 are cut to match the angle 8 given by Equation 11 such that the metal surfaces of the corrugations are parallel to the incident partial wavefront 15.
  • waves that reflect off a surface add on the curvature of the surface to the existing curvature of the wave ⁇ front. If the surface is parallel to the partial wave- front, the' wave is returned in the direction from which it came.
  • the reflected partial wavefront will maintain the original mode shape as long as the surface between the corrugations, namely the intervening base 17 between adjacent reflecting corrugations matches the original mode boundary, i.e., the waveguide wall 18.
  • the bases 17 should be smooth, thereby allowing undistorted propagation of forward scattered partial wavefronts. It is preferred that opposing corrugations are aligned with their peaks in line in a vertical plane tranverse to the longitudinal axis of the hollow cylindrical member, to allow ideal matching, of the waveguide modes.
  • the partial wavefronts scattered from each of the surface corrugation 14 elements combine and power is consequently scattered predominantly into those grating orders which are aligned with the local scattering angles of the surfaces. Since the retro- - reflection condition of Equations 1 through 5 have been met, the scattered power is predominantly reflected into an identical mode travelling in the reverse direction.
  • a design technique for a cylindrical corrugated reflector based on the foregoing parameters could be as ollows :
  • k c will be determined from the diameter of the waveguide
  • Equation (11) is then determined from Equation (11); 6.
  • d is then determined from Equation (4); alternatively, d could be determined from the longitudinal half-wavelength of the mode being reflected.
  • Determination of the parameters d and ⁇ using the foregoing technique provides a design technique for a corrugated reflector which will coherently reflect power at wavelength ⁇ .
  • the reflectivity has been measured to reach as high as 0.99 with as few corrugations as twelve, each reflector constituting an actual percent of 20% of the open area of the waveguide.
  • the resulting resonator 16 is a cylindrical high-Q device which does not obstruct the passage of 5 an axial electron beam, thereby making it suitable for using in an FEL.
  • the Q was measured at over 10,000 at 30 GHz while maintaining phase coherence of at least the TE]_ ⁇ mode.
  • the preferred embodiment of the instant invention would have been expected to result in lower reflectivity because the reflecting sides of the adjacent triangular corrugations are separated by intervening bases and 5 therefore offer shorter sloping reflecting surfaces for a given d, than would be the case if the sides of adjacent corrugations were allowed to extend and contact each other without an intervening base. This is distinguished from the Yariv article.
  • the instant reflector design is both compact and efficient, and the experimental results, discussed above indicate that the preferred reflector configuration of the present invention actually results in higher reflectivity at specific wavelengths. Moreover,
  • the parameters need to be determined; specifically, the number of corrugations 14 in each reflector 10, as well as the length of the waveguide 18.
  • the length of the waveguide 18 it should optimally be an integer number of half wavelengths to keep the reflections from the reflectors 10 in phase . In this manner, the overall length of the resonator 16 will match the resonance created by the reflectors 10.
  • the minimum number M of corrugations 14 of each reflector 10 in the resonator 16 that number is determined from the following relationships:
  • the number of corrugations 14 is also dependent on the reflection coefficient of - the reflector 10, and satisfying Equation (13) will generally ensure an approximately correct relationship between the reflection coefficient and the number of corrugations; typically the minimum number of corrugations is m.
  • the radius of the waveguide is given as r - (N+l) sin 8 A
  • Equation 11 the shape of corrugation. 14 can be allowed to deviate from the ideal blaze angle by several degrees, thereby relaxing the condition imposed by Equation 11 correspondingly.
  • FIG. 6 An FEL 20 utilizing the advantageous properties of the blazed reflectors 10 just described is shown in FIG. 6.
  • the resonator 16 utilizes the corrugated reflectors 10 instead of the conventional metal mirrors.
  • the FEL 20 is comprised of an electron gun 22 producing an electron beam 30, a focusing pole piece 24, a guide field solenoid 26, an out-coupling horn 28, an output window 32, a depressed collector 34, high-voltage bushings 36 and 40, and a magnetic wiggler 38.
  • the configuration and operation of the FEL 20, with the exception of the reflectors 10, is conventional. In a prototype FEL constructed with the corrugated reflectors, 60 kw of output power was produced at 30.75 GHz.

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  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Engineering & Computer Science (AREA)
  • Plasma & Fusion (AREA)
  • Optics & Photonics (AREA)
  • Lasers (AREA)

Abstract

Le réflecteur strié à échelles (10) possède des stries ou rainures internes, disposées à des angles spécifiques, et réfléchit de manière cohérente une énergie à des longueurs d'onde spécifiques. Les stries (14) satisfont aux critères de rétroréflexion selon les conditions de Bragg pour des réseaux, en éliminant des modes de réflexion d'ordre supérieure, et en maximisant la rétroréflexion et en minimisant la dispersion vers l'avant selon la conception de l'échelle. Deux de ces réflecteurs peuvent être agencés de manière à former un résonateur à laser (16) en les plaçant aux extrémités opposées d'un guide d'onde d'adaptation. Le réflecteur n'obstrue pas le passage d'un faisceau électronique axial (30) et permet ainsi la mise en oeuvre de la partie résonateur d'un laser à électrons libres (20).
PCT/US1987/000671 1986-05-09 1987-03-30 Reflecteur strie et procede pour laser a electrons libres WO1987007092A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
DE8787902965T DE3781089T2 (de) 1986-05-09 1987-03-30 Gewellte reflektor-vorrichtung und freielektronenlaser-verfahren.

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US861,764 1986-05-09
US06/861,764 US4697272A (en) 1986-05-09 1986-05-09 Corrugated reflector apparatus and method for free electron lasers

Publications (1)

Publication Number Publication Date
WO1987007092A1 true WO1987007092A1 (fr) 1987-11-19

Family

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Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/US1987/000671 WO1987007092A1 (fr) 1986-05-09 1987-03-30 Reflecteur strie et procede pour laser a electrons libres

Country Status (5)

Country Link
US (1) US4697272A (fr)
EP (1) EP0266395B1 (fr)
JP (1) JPS63503347A (fr)
DE (1) DE3781089T2 (fr)
WO (1) WO1987007092A1 (fr)

Families Citing this family (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4912367A (en) * 1988-04-14 1990-03-27 Hughes Aircraft Company Plasma-assisted high-power microwave generator
US4939740A (en) * 1988-06-07 1990-07-03 General Atomics Cyclotron autoresonance maser with helical electron guiding center
US5302962A (en) * 1988-12-05 1994-04-12 European Atomic Energy Community (Euratom) Antenna system producing a millimeter wave beam having a gaussian-like distribution
US4888776A (en) * 1988-12-13 1989-12-19 Hughes Aircraft Company Ribbon beam free electron laser
US5023563A (en) * 1989-06-08 1991-06-11 Hughes Aircraft Company Upshifted free electron laser amplifier
JP2756735B2 (ja) * 1991-05-31 1998-05-25 日本電気エンジニアリング株式会社 レーザ共振器
US5243618A (en) * 1991-11-22 1993-09-07 Hughes Aircraft Company Cavity resonator incorporating waveguide filter
IL108439A (en) * 1994-01-26 1998-08-16 Yeda Res & Dev Optically pumped laser apparatus
JP2981543B2 (ja) * 1997-10-27 1999-11-22 金沢大学長 電子管型一方向性光増幅器
US6574248B1 (en) * 1999-11-22 2003-06-03 The United States Of America As Represented By The Secretary Of The Army Laminated wigglers
US7233297B1 (en) 2004-07-13 2007-06-19 Hrl Laboratories, Llc Steerable radial line slot antenna
US11289784B2 (en) * 2020-07-10 2022-03-29 Lockheed Martin Corporation Multipaction-proof waveguide filter

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4367551A (en) * 1980-07-15 1983-01-04 The United States Of America As Represented By The Secretary Of The Air Force Electrostatic free electron laser
US4438513A (en) * 1981-01-26 1984-03-20 The United States Of America As Represented By The Secretary Of The Navy Short wavelength free electron laser using low energy electrons

Non-Patent Citations (4)

* Cited by examiner, † Cited by third party
Title
Applied Physics B. Photo Physics and Laser Chemistry, Volume B-33, No. 3, March 1984, (Heidelberg, DE), H.P. PREISWERK et al.: "Group Theory and Experiments on Helical and Linear Distributed Feedback gas Lasers", pages 115-131 see paragraph 1.3; figure 1 *
IEEE Journal of Quantum Electronics, Volume QE-13, No. 4, April 1977, (New York, US), A. YARIV et al.: "Periodic Structures for Integrated Optics", pages 233-251 see page 250, column 2, lines 32-42; figure 35 cited in the application *
IEEE Journal of Quantum Electronics, Volume QE-13, No. 4, April 1977, (New York, US), W. STREIFER et al.: "Coupled Wave Analysis of DFB and DBR Lasers", pages 134-145 see Abstract; page 134, column 2, line 22 - page 135, column 1, line 2; page 137, column 2, lines 20-30; figure 2 *
IEEE Journal of Quantum Electronics, Volume QE-19, No. 3, March 1983, (New York, US), V.L. BRATMAN et al.: "FEL's with Bragg Reflection Resonators: Cyclotron Autoresonance Masers Versus Ubitrons" pages 282-295 see figures 2,12 cited in the application *

Also Published As

Publication number Publication date
DE3781089T2 (de) 1993-02-04
EP0266395A1 (fr) 1988-05-11
DE3781089D1 (de) 1992-09-17
JPS63503347A (ja) 1988-12-02
US4697272A (en) 1987-09-29
EP0266395B1 (fr) 1992-08-12

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